U.S. patent number 9,580,312 [Application Number 14/758,649] was granted by the patent office on 2017-02-28 for method for producing acetylenes and syngas.
This patent grant is currently assigned to BASF SE. The grantee listed for this patent is BASF SE. Invention is credited to Kai Rainer Ehrhardt, Dirk Grossschmidt, Michael L. Hayes, Horst Neuhauser, Michael Russ, Maximilian Vicari, Christian Weichert.
United States Patent |
9,580,312 |
Vicari , et al. |
February 28, 2017 |
Method for producing acetylenes and syngas
Abstract
The invention relates to a continuous method for producing
acetylenes and syngas by partially oxidizing hydrocarbons with
oxygen. A first feed stream (1) containing one or more hydrocarbons
and a second feed stream (2) containing oxygen are --mixed in a
ratio of the mass flows of the second feed stream (2) to the first
feed stream (1) corresponding to an oxygen number of less than or
equal to 0.31, said streams being heated separately from each
other, --and fed to a combustion chamber (FR) via a burner block
(BR), the partial oxidation of the hydrocarbons being carried out
in said combustion chamber, --thereby obtaining a first cracked gas
stream I.sub.g. The invention is characterized in that --the first
cracked gas stream I.sub.g is precooled to a temperature ranging
from 100 to 1000.degree. C. in a prequench region (H), thereby
obtaining a second cracked gas stream II.sub.g, --50 to 90% of the
solids contained in the second cracked gas stream II.sub.g are
separated therefrom in a solid-gas separating device (A), thereby
obtaining a solid stream I.sub.f and a third cracked gas stream
III.sub.g, --the third cracked gas stream III.sub.g is cooled to 80
to 90.degree. C. by injecting water in a total quench region (B),
thereby obtaining a fourth cracked gas stream IV.sub.g and a first
process water stream I.sub.liq, --the fourth cracked gas stream
IV.sub.g undergoes a fine separation of solids in one or more
scrubbing devices (C, D), thereby obtaining one or more process
water streams II.sub.liq, III.sub.liq and a product gas stream
VI.sub.g, --the process water streams I.sub.liq, II.sub.liq,
III.sub.liq are merged into a combined process water stream
IV.sub.liq, --the combined process water stream IV.sub.liq is
partly recirculated, as stream V.sub.liq, into the total quench
region (B) and otherwise undergoes a cleaning process, as stream
VI.sub.liq, by means of a partial evaporation process, thereby
obtaining a cleaned process water stream VII.sub.liq, --which is
cooled by a recooling device (F), partially recycled, as stream
VIII.sub.liq, into the method, and otherwise discharged, as stream
IX.sub.liq.
Inventors: |
Vicari; Maximilian
(Limburgerhof, DE), Weichert; Christian (Bad
Duerkheim, DE), Grossschmidt; Dirk (Mannheim,
DE), Russ; Michael (Roemerberg, DE),
Ehrhardt; Kai Rainer (Speyer, DE), Neuhauser;
Horst (Dudenhofen, DE), Hayes; Michael L.
(Gonzales, LA) |
Applicant: |
Name |
City |
State |
Country |
Type |
BASF SE |
Ludwigshafen |
N/A |
DE |
|
|
Assignee: |
BASF SE (Ludwigshafen,
DE)
|
Family
ID: |
50023542 |
Appl.
No.: |
14/758,649 |
Filed: |
January 15, 2014 |
PCT
Filed: |
January 15, 2014 |
PCT No.: |
PCT/EP2014/050652 |
371(c)(1),(2),(4) Date: |
June 30, 2015 |
PCT
Pub. No.: |
WO2014/111396 |
PCT
Pub. Date: |
July 24, 2014 |
Prior Publication Data
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Document
Identifier |
Publication Date |
|
US 20150336858 A1 |
Nov 26, 2015 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61753019 |
Jan 16, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C01B
3/36 (20130101); C07C 2/78 (20130101); C07C
2/78 (20130101); C07C 11/24 (20130101); C01B
2203/062 (20130101); C01B 2203/148 (20130101); C01B
2203/0894 (20130101); C01B 2203/0877 (20130101); C01B
2203/0255 (20130101); C01B 2203/025 (20130101); C01B
2203/1235 (20130101) |
Current International
Class: |
C01B
3/38 (20060101); C07C 2/78 (20060101); C01B
3/36 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1 989 160 |
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Nov 2008 |
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EP |
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WO 2007/096271 |
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Aug 2007 |
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WO |
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WO 2007096271 |
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Aug 2007 |
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WO |
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WO 2012/062584 |
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May 2012 |
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WO |
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WO 2012/062784 |
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May 2012 |
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WO |
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WO 2012062784 |
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May 2012 |
|
WO |
|
Other References
International Search Report and Written Opinion issued Apr. 4, 2014
in PCT/EP2014/050652. cited by applicant .
Ullmann's Encyclopedia of Industrial Chemistry, vol. A1, 1984, pp.
97-145 (with Cover Page). cited by applicant .
Peter Passler, et al., "Acetylene" Ullmann's Encyclopedia of
Industrial Chemistry, XP002722234, Oct. 15, 2011, pp. 284-293 (with
Intro page). cited by applicant.
|
Primary Examiner: Mayes; Melvin C
Assistant Examiner: Vaden; Kenneth
Attorney, Agent or Firm: Oblon, McClelland, Maier &
Neustadt, L.L.P.
Claims
The invention claimed is:
1. A continuous process for preparing acetylene and synthesis gas
by partial oxidation of hydrocarbons with oxygen, comprising:
separately heating in preheaters a first input stream comprising
one or more hydrocarbons and a second input stream comprising
oxygen, mixing in a mixing unit the first and second input streams
in a ratio of mass flow of the second to first input stream
corresponding to an oxygen ratio of less than or equal to 0.31,
wherein the oxygen ratio is the amount of oxygen present in the
second input stream to the amount of oxygen which is needed
stoichiometrically for full combustion of one or more hydrocarbons
in the first input stream, supplying said mixture of the first and
second streams via a burner block to a combustion chamber
configured for partial oxidation of the one or more hydrocarbons,
thus obtaining a first cracking gas stream I.sub.g; cooling in a
prequench said first cracking gas stream I.sub.g by injecting an
aqueous quench medium to a temperature of 100 to 1,000.degree. C.,
thus obtaining a second cracking gas stream II.sub.g; removing in a
solid-gas separation apparatus 50 to 90% of the solids present in
the second cracking gas stream II.sub.g thus obtaining a solids
stream I.sub.f and a third cracking gas stream III.sub.g, cooling
in a total quench the third cracking gas stream III.sub.g by
injecting water to a temperature of 80 to 90.degree. C. to obtain a
fourth cracking gas stream IV.sub.g and a first process water
stream I.sub.liq, scrubbing in one or more scrubbing apparatuses
the fourth cracking gas stream IV.sub.g to remove solids, thus
obtaining process water streams II.sub.liq, or II.sub.liq and
III.sub.liq, and a product gas stream VI.sub.g, combining process
water streams I.sub.liq, II.sub.liq, III.sub.liq thus providing a
combined process water stream IV.sub.liq, recycling the combined
process water stream IV.sub.liq partly as stream V.sub.liq into the
total quench and partly as stream VI.sub.liq to cleaning by partial
vaporization in a one-stage flash vessel that being vaporizes
stream VI.sub.liq in a proportion of 0.01 to 10% by weight, based
on the total weight thereof, to obtain a cleaned process water
stream VII.sub.liq, cooling with a re-cooling device cleaned
process water stream VII.sub.liq and partly recycling it as stream
VIII.sub.liq into one or more of the one or more scrubbing
apparatuses, and partly discharging the rest as stream
IX.sub.liq.
2. The continuous process according to claim 1, wherein stream
IX.sub.liq is discharged at a flow rate corresponding to the water
of reaction obtained in the partial oxidation of the hydrocarbons
with oxygen.
3. The continuous process according to claim 1, wherein 60 to 80%
of the solids present in the second cracking gas stream II.sub.g is
separated therefrom in the solid-gas separation apparatus.
4. The continuous process according to claim 1, wherein the solids
stream I.sub.f comprises tars, soots and cokes.
5. The continuous process according to claim 1, wherein the
solid-gas separation apparatus is a cyclone separator.
6. The continuous process according to claim 1, wherein the first
cracking gas stream I.sub.g is cooled in the prequench to a
temperature in the range from 200 to 650.degree. C.
7. The continuous process according to claim 6, wherein the first
cracking gas stream I.sub.g is cooled in the prequench to a
temperature in the range from 250 to 400.degree. C.
8. The continuous process according to claim 1, wherein the
prequench is a water quench.
9. The continuous process according to claim 8, wherein the
prequench comprises a heat exchanger for extracting heat of
reaction in the form of high-pressure steam.
10. The continuous process according to claim 1, wherein the one or
more scrubbing apparatuses comprise a first scrubbing apparatus
used is a Venturi scrubber and the second scrubbing apparatus a
quench column.
11. The continuous process according to claim 1, wherein the one or
more scrubbing apparatuses comprise a first and second scrubbing
apparatus, and wherein the cleaned process water substream
VIII.sub.liq is supplied to the second scrubbing apparatus.
12. The continuous process according to claim 1, wherein the
re-cooling device is a closed re-cooling device.
13. The continuous process according to claim 1, wherein the
re-cooling device is an open cooling tower.
Description
The present invention relates to a process for preparing acetylene
and synthesis gas by partial oxidation of hydrocarbons with
oxygen.
The above partial oxidation is a high-temperature reaction which is
typically conducted in a reactor system comprising a mixing unit, a
burner block and a quench unit, and is described, for example, in
Ullmanns Encyclopedia of Industrial Chemistry (5.sup.th Edition,
Volume A1, pages 97-144).
According to Ullmanns Encyclopedia of Industrial Chemistry
(5.sup.th Edition, Volume A1, pages 97-144), the feedstocks are
heated separately in preheaters. The heated feedstocks are mixed in
a mixing unit and supplied via a mixing diffuser to a burner and
further to a combustion chamber. Downstream of the combustion
chamber, nozzles are used to supply an aqueous quench medium to the
cracking gas, which is cooled rapidly to about 80-90.degree. C.
Through suitable selection of the oxygen ratio .lamda.
(.lamda.<0.31), the process is conducted such that the yield of
acetylene based on the dry cracking gas is at an optimum (>8%).
In this context, oxygen ratio .lamda. is understood to mean the
ratio of the amount of oxygen actually present to the
stoichiometrically necessary amount of oxygen required for the full
combustion of the feedstocks. At the same time, the soot loading of
the cracking gas is also at a maximum. The soot formed from the gas
phase in the combustion chamber is partly precipitated by the
quench, in a downstream cooling column and a downstream
electrostatic filter. The product gas stream containing products of
value is removed separately via the cooling column. Downstream of
the electrostatic filter, the soot concentration in the remaining
cracking gas (without products of value) has fallen to about 1
mg/m.sup.3. The soot present in the process water from the quench,
the cooling column and the electrostatic filter has a high
hydrocarbon content and is therefore hydrophobic, which causes it
to float on the process water. Therefore, this soot-laden process
water is passed through what are called open soot channels with
surface particulate precipitators. The floating soot components are
removed and sent to firing. The process water cleaned therein is
subsequently run through an open cooling tower and thus cooled. In
the course of this, and during the solid-liquid separation
beforehand, a majority of the hydrocarbons bound in liquid and
gaseous form in the process water, especially aromatics, alkynes,
benzene-toluene-xylene, etc., is emitted into the ambient air
together with portions of the process water. Subsequently, the loss
of process water which has thus arisen is compensated for by
addition and the water circuit is closed in the direction of
cooling column and quench.
The emissions of hydrocarbons from the process water from the
cooling tower (i.e. in an open process water mode), however, are no
longer acceptable under the applicable environmental protection
regulations. Nor is a closed process water mode an acceptable
solution, since the hydrocarbons would accumulate here and lead to
polymerization and blockage of the plant.
A further emission source is that of the open soot channels. The
solids deposited in the soot channels from the process water have
to be dried in a complex manner prior to possible commercial
marketing, which makes them unattractive.
A further process for preparing acetylene and synthesis gas by
partial oxidation of hydrocarbons with oxygen is described in U.S.
Pat. No. 5,824,834. This is a closed water quench process which is
optimized for soot volumes and is operated with a lean feed stream,
specifically with a feed stream having an oxygen ratio
.lamda.>0.31. However, the process has the disadvantage of a
reduced yield of acetylene product of value.
In this process variant, the aqueous quench medium is likewise
supplied by means of nozzles to the cracking gas which is cooled
rapidly to about 80-90.degree. C. The soot formed from the gas
phase in the combustion chamber is partly precipitated by the
quench, a downstream cooling column operated with recirculating
water, and a downstream electrostatic filter. The product gas
stream containing products of value is removed separately via the
cooling column. The process is operated here through selection of
the oxygen ratio .lamda. (.lamda.>0.31) such that the soot
volume obtained in the cracking gas is so low that solely the
discharge of the water of reaction obtained from the incineration
can ensure steady-state operation. This, however, reduces the
acetylene content in the dry cracking gas by 2 percentage points
compared to the above-described process, to about 6% by volume.
This enables a closed water quench mode, i.e. one isolated from the
environment. The advantage over the above-described process variant
is thus the possibility of closed operation without further
separation apparatus. The disadvantage is yield losses based on the
acetylene product of value and target product. In addition, it is
likewise the case that the solids separated out of the process
water have to be dried in a complex manner prior to possible
commercial marketing, which makes them unattractive.
A third process for preparing acetylene and synthesis gas by
partial oxidation of hydrocarbons with oxygen is described in EP-A
12171956. This is a process which combines the advantages of the
two above-described processes, i.e. optimized yield of acetylene
product of value according to Ullmanns Encyclopedia of Industrial
Chemistry, 5th Edition, Volume A1, pages 97-144 and compliance with
applicable environmental protection regulations in accordance with
U.S. Pat. No. 5,824,834, and its aim is formulated as being that of
minimizing disadvantages, i.e. outdated non-compliance with
environmental protection regulations in the first process above and
distinct yield losses in the second process above. It should be
pointed out here that, according to Ullmanns Encyclopedia of
Industrial Chemistry (5th Edition, Volume A1, pages 97-144) the
amounts both of soot, coke and tar obtained and of higher alkynes
and naphthalene rise in a greater-than-proportional manner in the
case of modes of operation with oxygen ratios of .lamda.<0.31,
and can no longer be removed and retained to a sufficient degree by
the separation concepts described in U.S. Pat. No. 5,824,834 in
order to fulfill the applicable environmental protection
regulations.
A further process for preparing acetylene and synthesis gas by
partial oxidation of hydrocarbons with oxygen is described in EP-A
1 989 160. This is an extension of the process of U.S. Pat. No.
5,824,834, such that the remaining very fine solid components
(soot, tar, coke) in the product gas are separated out by means of
product gas compressors. In this case, the solids obtained in the
already pre-purified product gas separate out in the cooling water
injected directly into the product gas compressor and are
discharged therefrom. However, a disadvantage is that the solids
obtained are discharged here bound within the water. For commercial
(dry) marketing of the solids, this entails an inconvenient and
costly aftertreatment in the form of drying, which generally
opposes commercially attractive marketing for reasons of cost.
Therefore, in the context of the European patent application with
application number EP 12171956.1, essentially the combination of
the three process concepts from Ullmanns Encyclopedia of Industrial
Chemistry (5th Edition, Volume A1, pages 97-144), U.S. Pat. No.
5,824,834 and EP-A 1 989 160 is described. Additionally described
is the separation of liquid and gaseous unwanted by-products
(essentially higher alkynes and naphthalene) by means of partial
vaporization (flash).
However, the above prior art does not give any pointer to the
problem of the increased occurrence of soot, coke and tar, and how
these can be separated out in dry form.
It was accordingly an object of the invention to provide a process
for preparing acetylene and synthesis gas by partial oxidation of
hydrocarbons which combines the advantages of the above processes,
i.e. ensures both a high yield of acetylene product of value and
compliance with the applicable environmental protection regulations
through sufficient separation and retention of unwanted gaseous
and/or liquid by-products, and which additionally enables
sufficient dry removal and retention of solid unwanted by-products
(tar, coke, soot).
The object is achieved by a continuous process for preparing
acetylene and synthesis gas by partial oxidation of hydrocarbons
with oxygen, in which a first input stream comprising one or more
hydrocarbons and a second input stream comprising oxygen are
separately heated in preheaters, mixed in a mixing unit in a ratio
of the mass flow of the second input stream to the first input
stream corresponding to an oxygen ratio of less than or equal to
0.31, the oxygen ratio being understood to mean the ratio of the
amount of oxygen actually present in the second input stream to the
amount of oxygen which is needed stoichiometrically and is required
for the full combustion of the one or more hydrocarbons present in
the first input stream, supplied via a burner block to a combustion
chamber in which the partial oxidation of the hydrocarbons takes
place, to obtain a first cracking gas stream I.sub.g, wherein the
first cracking gas stream I.sub.g is cooled in a prequench by
injection of an aqueous quench medium to a temperature in the range
from 100 to 1000.degree. C. to obtain a second cracking gas stream
II.sub.g, in a solid-gas separation apparatus, 50 to 90% of the
solids present in the second cracking gas stream II.sub.g are
removed therefrom to obtain a solids stream I.sub.f and a third
cracking gas stream III.sub.g, the third cracking gas stream
III.sub.g is cooled in a total quench by injection of water to 80
to 90.degree. C. to obtain a fourth cracking gas stream IV.sub.g
and a first process water stream I.sub.liq, the fourth cracking gas
stream IV.sub.g is subjected in one or more scrubbing apparatuses
to a fine removal of solids to obtain one or more process water
streams II.sub.liq, III.sub.liq and a product gas stream VI.sub.g,
the process water streams I.sub.liq, II.sub.liq, III.sub.liq are
combined to give a combined process water stream IV.sub.liq, the
combined process water stream IV.sub.liq is recycled partly as
stream V.sub.liq into the total quench and the rest is subjected as
stream VI.sub.liq to cleaning by partial vaporization in a
one-stage flash vessel, stream VI.sub.liq being vaporized in a
proportion of 0.01 to 10% by weight, based on the total weight
thereof, to obtain a cleaned process water stream VII.sub.liq which
is cooled by means of a re-cooling device, partly recycled as
stream VIII.sub.liq into one or more of the one or more scrubbing
apparatuses, and the rest is discharged as stream IX.sub.liq, and
supplied to the wastewater in need of treatment.
It has been found that the inventive process regime, through
prequenching of the cracking gas stream from a process for
continuously preparing acetylene and synthesis gas to a temperature
in the range from 100 to 1000.degree. C., avoids both unwanted
condensation of water of reaction, quench water or tars prior to
supply of the cracking gas stream obtained here to a downstream
solid-gas separation apparatus, and thermal overloading of the
solid-gas separation apparatus, and can additionally ensure
stoppage of the synthesis reaction and hence an optimal acetylene
yield.
By operating the solid-gas separation apparatus in accordance with
the invention, in such a way that 50 to 90% of the solids from the
cracking gas stream obtained in the prequench are removed therein,
the amount of soot remaining in the cracking gas is so small that
solely the discharge of a substream of the cleaned process water
stream, especially in a flow rate corresponding to the water of
reaction obtained from the partial oxidation of hydrocarbons with
oxygen, into the wastewater in need of treatment can ensure
steady-state, continuous operation of the plant.
It has been found that, surprisingly, by virtue of a further simple
solid-gas separation apparatus connected downstream of the
prequench, the total solids separation rate into the process water
is sufficiently high, and hence obviates the need for an additional
removal in a solid-gas separation apparatus, operated in a costly
and inconvenient manner and with a high energy demand, in the form
of an electrostatic filter. In addition, the proposed concept for
solids separation makes the solids content in the process water
obtained so low that continuous discharge of process water,
especially in an amount corresponding to the water of reaction
obtained in the partial oxidation of hydrocarbons with oxygen, into
the wastewater in need of treatment enables continuous operation of
the process without further, complex and water-intensive
solid-liquid separation devices (soot channels).
The process according to the invention is independent of the
specific form of the reactor system used, comprising mixing unit,
burner block and quench unit.
The preferred reactor systems typically used are explained in
detail hereinafter:
The starting materials, i.e. a first input stream comprising
hydrocarbons, especially natural gas, and a second gas stream
comprising oxygen, are heated separately, typically up to
600.degree. C. In a mixing unit, the reactants are mixed vigorously
and, after flowing through a burner block, are reacted
exothermically in a combustion chamber. The burner block typically
consists of a multitude of parallel channels in which the flow rate
of the ignitable oxygen/hydrocarbon mixture is higher than the
flame speed, in order to prevent the flame from striking through
into the mixing unit. The metallic burner block is cooled in order
to withstand the thermal stresses. According to the residence time
in the mixing unit, there is the risk of pre- and re-ignition due
to the limited thermal stability of the mixtures. For this purpose,
the term "ignition delay time" or "induction time" is used as the
period of time within which an ignitable mixture does not undergo
any significant intrinsic thermal change. The induction time
depends on the nature of the hydrocarbons used, the mixing state,
pressure and temperature. It determines the maximum residence time
of the reactants in the mixing unit. Reactants such as hydrogen,
liquefied gas or light gasoline, the use of which is particularly
desirable due to yield and/or capacity increases in the synthesis
process, feature comparatively high reactivity and hence a short
induction time.
The acetylene burners being used on the current production scale
are notable for the cylindrical geometry of the combustion chamber.
The burner block has passage bores preferably in a hexagonal
arrangement. In one embodiment, for example, 127 bores of internal
diameter 27 mm are arranged hexagonally on a circular base cross
section with a diameter of approx. 500 mm. In general, the channel
diameters used are about 19 to 27 mm in diameter. The downstream
combustion chamber in which the flame of the partial oxidation
reaction, which forms acetylene and synthesis gas, is stabilized is
typically likewise of cylindrical cross section, is water-cooled
and corresponds in terms of appearance to that of a short tube, for
example of diameter 180 to 533 mm and length 380 to 450 mm. At the
level of the burner block, what is called auxiliary oxygen is
supplied to the combustion chamber both in the axial and in the
radial direction. This ensures flame stabilization and hence a
defined separation of the flame roots and hence of the commencement
of reaction from the stopping of the reaction by the quench
unit.
The overall burner composed of burner block and combustion chamber
is preferably suspended from the top by means of a flange into a
quench vessel of greater cross section. At the level of the exit
plane from the combustion chamber, on the outer circumference
thereof, are installed quench nozzles on one or more quench
distributor rings, which atomize the quench medium with or without
the aid of an atomization medium and inject it virtually at right
angles to the main flow direction of the reaction gases leaving the
combustion chamber. This direct quench has the task of cooling the
reaction mixture extremely rapidly, such that further reactions,
i.e. especially the degradation of acetylene formed, are frozen.
The range and distribution of the quench jets is ideally such that
a very homogeneous temperature distribution is achieved within a
very short time.
The present industrial process forms, as well as acetylene,
essentially hydrogen, carbon monoxide and soot. The soot particles
formed in the flame front can adhere as seeds to the combustion
chamber side walls, which then results, under suitable
physicochemical conditions, in growth, deposition and caking of
coke layers.
These deposits are removed by mechanical cleaning periodically in
the region of the combustion chamber walls by means of a poker
unit, as described, for example, in Ullmanns Encyclopedia of
Industrial Chemistry 5th Edition, Volume A1, pages 97-144 or in
U.S. Pat. No. 5,824,834.
For a further preferred embodiment, the reactor system has a
flushed reactor side wall as described in WO-A 2012/062784, or a
flushed reactor end face as described in WO-A 2012/062584. In these
embodiments, the above-described mechanical poking can be dispensed
with, and this avoids entrainment of large-scale solid portions
downstream and hinders the continuation of the process there--for
example through blockage of separation and/or heat exchanger
apparatuses.
In an advantageous embodiment, 60 to 80% of the solids present in
the second cracking gas stream II.sub.g are separated therefrom in
the solid-gas separation apparatus.
The solids stream I.sub.f separated out in the solid-gas separation
apparatus comprises predominantly tars, soots and cokes.
The solid-gas separation apparatus is advantageously a cyclone
separator.
Advantageously, the first cracking gas stream I.sub.g is cooled in
the prequench to a temperature in the range from 200 to 650.degree.
C.
Further advantageously, the first cracking gas stream I.sub.g is
cooled in the prequench to a temperature in the range from 250 to
400.degree. C.
The prequench is advantageously a water quench.
A particularly advantageous embodiment in terms of energy is one in
which the prequench comprises a heat exchanger for extracting heat
of reaction in the form of high-pressure steam.
Preferably, the first scrubbing apparatus used is a Venturi
scrubber and the second scrubbing apparatus a quench column.
The cleaned process water substream VIII.sub.liq is preferably
recycled into the second scrubbing apparatus.
In a preferred embodiment, the re-cooling device is a closed
re-cooling device.
In a further preferred embodiment, the re-cooling device is an open
cooling tower. In this process variant, the entire cleaned process
water stream is preferably recycled into the process.
The invention is illustrated hereinafter by a drawing and by
working examples.
FIG. 1 shows the schematic diagram of a preferred plant design of
the invention.
The preferred plant shown in FIG. 1 for performance of the process
according to the invention is supplied with a first input stream 1
comprising one or more hydrocarbons, and a second oxygen-comprising
input stream 2, these being preheated separately by means of
preheaters V1 and V2, mixed in a mixing unit M, supplied via a
burner block BR to a combustion chamber FR to obtain a first
cracking gas stream I.sub.g, which is supplied to a prequench H and
quenched therein by injecting an aqueous quench medium, not shown
in the FIGURE to 100 to 1000.degree. C. In the preferred embodiment
shown in the FIGURE, this extracts heat of reaction from the
prequench H in the form of high-pressure stream. The second
cracking gas stream II.sub.g which leaves the prequench H is
supplied to a solid-gas separation apparatus A which is designed
such that 50 to 90% of the solids present in the second cracking
gas stream II.sub.g especially soots, tars and cokes, are removed
therein to obtain a solids stream I.sub.f, which is drawn off, and
a third cracking gas stream III.sub.g, which is supplied to a total
quench B and is cooled therein by direct water injection to 80 to
90.degree. C. to obtain a fourth cracking gas stream IV.sub.g and a
first process water stream I.sub.liq. In the preferred embodiment
shown in the FIGURE, the fourth cracking gas stream IV.sub.g is
supplied to a first scrubbing apparatus C, and separated therein
into a fifth cracking gas stream V.sub.g and a second process water
stream II.sub.liq The cracking gas stream V.sub.g is supplied to a
second scrubbing apparatus D and separated therein into a product
gas stream VI.sub.g and a further process water stream III.sub.liq
The process water streams I.sub.liq, II.sub.liq, III.sub.liq are
combined to give a combined process water stream IV.sub.liq, which
is recycled partly as process water stream V.sub.liq into the total
quench B and the rest is supplied as process water stream
VI.sub.liq to a one-stage flash vessel E, in which partial
vaporization is effected to obtain a cleaned process water stream
VII.sub.liq, which is cooled by means of a re-cooling device F and
partly discharged via a valve G as process water stream IX.sub.liq,
and the rest, as process water stream VIII.sub.liq, in two
substreams in the preferred embodiment shown in the FIGURE, is
recycled into the second scrubbing apparatus D. The mass flow of
the process water stream IX.sub.liq is preferably adjusted such
that the amount of water which is obtained in the reaction, i.e.
the partial oxidation of hydrocarbons with oxygen, is
discharged.
The product gas stream VI.sub.g, as a product-of-value stream
comprising essentially acetylene, carbon monoxide and hydrogen, is
supplied as a crude product gas to a fine purification and product
gas separation, and fed into the corresponding chemical
value-addition chain.
WORKING EXAMPLES
Comparative Example
Without cleaning the process water to remove the gaseous and liquid
unwanted by-products, in a plant corresponding to the schematic
diagram in Ullmanns Encyclopedia of Industrial Chemistry 5th
Edition, Volume A1, pages 97-144, the following emissions are
obtained in specific terms from the open soot channels and the air
output of the cooling tower for 1 t of acetylene in the case of
performance of the partial oxidation with an oxygen ratio of
0.29:
TABLE-US-00001 Soot Cooling channels tower Total [kg] [kg] [kg] CO
0.303 0.363 0.667 methane 5.67E-02 8.46E-02 0.141 ethane 7.63E-03
1.21E-02 0.020 ethylene 6.80E-03 2.88E-02 0.036 acetylene 1.57E-01
6.05E+00 6.203 propene 5.16E-04 1.88E-03 0.002 propadiene 9.83E-04
3.58E-03 0.005 propyne 2.29E-03 1.01E-01 0.103 butenyne 1.65E-03
4.58E-02 0.047 butadiyne 7.39E-03 8.91E-01 0.898 benzene 2.29E-03
1.60E-01 0.162 naphthalene 5.14E-04 1.40E-02 0.014
In addition, 57 kg/t of acetylene are separated out of the process
water in wet form by means of soot channels and electrostatic
filters.
Working Example According to the Invention
In the performance of a partial oxidation of natural gas with
oxygen, at a ratio of the mass flow of the natural gas stream to
the oxygen-comprising gas stream corresponding to an oxygen ratio
of 0.29 and in accordance with achievement of a high yield, of
greater than 8%, of acetylene product of value, the prequench H was
considered to be a hot cyclone separator, the first scrubbing
apparatus C to be a Venturi scrubber and the second scrubbing
apparatus D to be a cooling column.
In the process, 65.57 kg of soot are formed per tonne of
acetylene.
In the case of a deposition level of 80% of the soot in the
prequench H, i.e. a dry deposition, a residual content of 13.11 kg
of soot per tonne of acetylene remains in the cracking gas
downstream of the prequench H.
In the case of a deposition level of 90% by means of wet fine
deposition in the Venturi scrubber C, 1.31 kg of soot per tonne of
acetylene remain in the cracking gas stream V.sub.g, which leaves
the Venturi scrubber C. In the case of further wet fine deposition
in the cooling column D, with a deposition level of 30%, a residual
content of 0.92 kg of soot per tonne of acetylene remains in the
cracking gas stream VI.sub.g, this being tolerable.
In the above process, 80% of the total solids content is thus
separated out of the cracking gas in dry form using a hot gas
cyclone as the prequench H, such that marketing thereof is possible
without further energy-intensive drying steps. In comparison to
this, only the remaining 20% of the solids content are separated
out in wet form by means of simple, high-efficiency separation
apparatuses, i.e. Venturi scrubber and cooling column. Soot
channels and electrostatic filters are no longer required as a
result. Solids separation by the process according to the invention
by means of a prequench results in such a low solids content in the
cleaned process water (13.11 kg of soot per tonne of acetylene),
that continuous discharge of a substream of the cleaned process
water, preferably according to the water of reaction obtained in
the partial oxidation, enables continuous operation of the process
without further, complex and water-intensive solid-liquid
separation devices, more particularly soot channels.
A similarly low proportion of solids in the process water has to
date been possible according to the prior art, for example in
accordance with U.S. Pat. No. 5,824,834, only in the case of a lean
mode of operation, i.e. with an oxygen ratio of 0.32 and
correspondingly with acceptance of a lower yield of acetylene of
only 6%.
Table 1 below reports the depletion by the cleaning step of the
removal of unwanted liquid and gaseous by-products in a cooling
tower in percent.
TABLE-US-00002 TABLE 1 Cooling tower Depletion kg/t of acetylene %
CO 1.20E-04 99.9820 methane 3.53E-05 99.9750 ethane 5.39E-06
99.9726 ethylene 3.55E-05 99.9002 acetylene 6.67E-02 98.9253
propene 1.99E-06 99.9172 propadiene 3.78E-06 99.9172 propyne
1.37E-03 98.6727 butenyne 3.90E-04 99.1785 butadiyne 3.62E-02
95.9707 benzene 3.36E-03 97.9296 naphthalene 1.01E-04 99.3007
Owing to the high depletion rate, the cooling tower can be replaced
by a closed heat exchanger without resulting in intolerable
accumulations of polymerizable components, especially of higher
acetylenes, in the process.
TABLE-US-00003 Secondary components in the process water Closed
water quench Closed water quench without flash with flash [ppm by
weight] [ppm by weight] CO 1.846 0.001 methane 0.430 0.000 ethane
0.061 0.000 ethylene 0.146 0.000 acetylene 30.537 0.333 propene
0.010 0.000 propadiene 0.018 0.000 propyne 0.514 0.007 butenyne
0.233 0.002 butadiyne 4.606 0.182 benzene 0.018 0.017 naphthalene
0.071 0.001
* * * * *